THE ANTIPREDATOR VOCALIZATIONS OF ADULT EASTERN SCREECH-OWLS

Adult eastern screech-owls (Otus asio) used six different vocalization s (bounce songs, whinny songs, bark calls, bark-screech calls, screech calls, and bill-claps) during trials in which a human approached nest sites or approached and handled nearly-fledged or recently-fledged yo ung. Bounce songs and whinny songs were uttered more frequently during nest defense trials while bark calls, screech calls and bill-claps we re uttered more frequently during trials with young owls. We suggest t hat bounce and whinny songs serve as low-intensity warnings to mates a nd nestlings. Bark calls consisted of a single, short duration note an d appear to serve as warning calls, informing a mate and young of an a pproaching predator and informing the predator of a willingness to att ack. Screech calls were short duration, high volume calls. Most screec h calls were given during flights directed at the predator, and may fu nction as a high-intensity warning call. Bark-screech calls appeared i ntermediate to bark and screech calls, both in structure and function. Most bill-claps were given during flights directed at the predator, o ften in conjunction with screech calls. We suggest that the combined v ocal signal of screech calls and bill-claps represents the highest-int ensity vocal warning directed at potential predators by screech-owls.